Humans think constantly about one another's thoughts, for example, in order to communicate, to teach, to learn from, to cooperate with, to compete with, and to deceive one another. This ability to fluently infer what others are thinking i impaired in individuals with Autism Spectrum Disorders (ASD), but the neural basis of this impairment is poorly understood. In particular, brain regions involved in thinking about other people's thoughts are not reliably smaller or less active in individuals with ASD. This proposal will test the possibilities that (i) reduced magnitude of activity, (ii) disorganization of the patern of activity, and/or (iii) altered connectivity of these brain regions that leads to social impairmets in ASD. We will test these hypotheses about the function of ToM regions in adults with ASD, in three key areas of ToM: understanding others' thoughts that are relevant for moral judgments (e.g. intentional vs. accidental harm), for inferring emotions, and for effective communication. Since ASD is a developmental disorder, it is critical to understand the developmental trajectory of these brain regions as well as their end state. Consequently, we will also test these hypotheses in children aged 5-12 years. We will also test whether the selectivity or pattern of activation in ToM brain regions changes over development. PUBLIC HEALTH RELEVANCE: Humans think constantly about one another's thoughts, for example, in order to communicate, to teach, to learn from, to cooperate with, to compete with, and to deceive one another. The ability to fluently infer what others are thinking is impaired in individuals with Autism Spectrum Disorders (ASD), but the neural basis of this impairment is poorly understood. This proposal will test the hypotheses that brain regions typically involved in thinking about other people's thoughts (i) are smaller or less active, (ii) have a disorganized pattern of activity, or (iii) have inappropriate connectivity, which leads to social impairments in adults and children with ASD.